The present invention relates to a rigid elongated member, a method of producing the elongated member and an apparatus for producing the elongated member, and in particular, to an elongated member for use in vehicles in which an impact force received from a direction crossing with an axial direction of the elongated member is resisted without deformation or buckling.
As an application example of such an elongated member, there can be listed a door beam (also referred to as a guard bar) attached to an inside portion of a door and a fender of an automobile for preventing the door from significantly deforming toward a chassis to protect a passenger when the automobile is subject to a collision from the side, a bumper reinforcement (also referred to as a bumper reinforcement member, or a bumper armature) attached onto an inside face of a plastic bumper or a bumper fascia arranged at a fore and a rear of the automobile for preventing deformation of the bumper or damage of the chassis when a collision occurs, or a roof rack (also referred to as a roof rail) attached onto a roof of the automobile with a pair of left and right members along a fore and rear direction or with fore and rear members along a widthwise direction for mounting baggage thereon.
Although there are other application examples for the rigid elongated member according to the present invention, the door beam will be explained hereinafter for the representative example thereof.
As a prior example relating to the present invention, for example, there is an official gazette of JP-A-4-238725 (hereinafter referred to as the prior example).
The prior example is constructed such that a fan-shaped bracket portion with a beam portion side as a pivot is disposed on both end sides of the beam portion in which the iron band is formed in the pipe-like manner by press-forming, and an attaching portion is formed on leading end portions of the bracket portion. The attaching portion is constructed such that uneven portions are formed alternately on the leading end portion in the widthwise direction.
In the construction of the above mentioned prior example, high strength steel sheet is used, and the length of the door beam is usually about 1 m (1.5 m for the bumper reinforcement, 2 m for the roof rack). A large sized press apparatus having a capacity of about 1000 ton is required in order to press-form the door beam integrally. The press die required for working this sheet is of a transferring-in-order type (progressive die), which is expensive.
Further, since a blank process is inevitably necessary for the press-working, a waste portion results which becomes a scrap in the plate material to be used.